Spin current generation with nano-oscillator

ABSTRACT

A device including a spin channel to transport a spin current, a nano-oscillator, and a magnetoresistive device that receives the spin current from the nano-oscillator. The nano-oscillator includes a magnetization state that oscillates between a first state and a second state in response to an input voltage or current. The oscillation of the nano-oscillator may induce the spin current within the spin channel. The magnetoresistive device includes a magnetization state that is set based at least in part on the received spin current.

This application is a divisional of U.S. patent application Ser. No.14/540,701, filed Nov. 13, 2014, the entire content of which isincorporated herein by reference.

GOVERNMENT INTEREST

This invention was made with government funds under Agreement No.HR0011-13-3-0002 awarded by DARPA. The U.S. Government has rights inthis invention.

TECHNICAL FIELD

The disclosure relates to spin pumping to generate spin current in aspin-based system.

BACKGROUND

In spin-based systems, a spin-polarized current is used to setmagnetization states of magnetoresistive devices. For example, throughthe spin-transfer torque (STT) effect, spin of electrons in aspin-polarized current can apply torque to a magnetic moment of a freelayer in a magnetoresistive device (e.g. a magnetic tunneling junction(MTJ), a giant magnetoresistive (GMR) device). Electrons are spinpolarized by the fixed layer of the magnetoresistive device. Dependingon the electron flow direction and relative orientation of spin ofelectrons and the magnetization of the free layer, magnetization of thefree layer can be set to be parallel or anti-parallel to themagnetization of the fixed layer.

One way to generate the spin-polarized current for setting magnetizationstates of magnetoresistive devices is through spin pumping. In spinpumping, a device injects a spin-polarized current into a spin channel,and the spin-polarized current drifts through the spin channel to one ormore magnetoresistive devices, and sets the magnetization states of theone or more magnetoresistive devices.

SUMMARY

The disclosure describes example techniques for spin pumping to generatea spin-polarized current with a spin transfer torque (STT)nano-oscillator to set magnetization states of one or moremagnetoresistive devices. The nano-oscillator is a type of amagnetoresistive device with a magnetic layer whose magnetization stateoscillates around a specific axis (determined by the effective magneticfield) in response to a current flowing through the nano-oscillator. Theoscillation of the magnetic layer of the nano-oscillator induces aspin-polarized current in a spin channel through spin pumping. A driftforce causes the spin-polarized current to flow through the spin channelto one or more magnetoresistive devices coupled to the spin channel, andthe spin-polarized current sets the magnetization state of themagnetoresistive devices.

In some examples, the spin pumping injects the spin-polarized currentdirectly into the spin channel, which reduces or eliminates the loss ofspin current caused by the impedance mismatch between the magnet and thespin channel, as compared other spin injection methods like lateral spinvalve devices. Moreover, the nano-oscillator, as described in thisdisclosure, may be scalable and tunable allowing for wider applicationas compared some other techniques that rely on a coplanar waveguide,with limited scalability, for spin pumping.

In one example, the disclosure describes a device including a spinchannel to transport a spin current, and a nano-oscillator having amagnetization state that, in response to an input voltage or current,oscillates between a first state and a second state and induces the spincurrent within the spin channel. The device also includes amagnetoresistive device that receives the spin current from thenano-oscillator, the magnetoresistive device having a magnetizationstate that is set by the received spin current.

In one example, the disclosure describes a method for generating a spincurrent and setting a magnetization state of a magnetoresistive device.The method includes applying an input voltage or current to anano-oscillator to oscillate a magnetization state of thenano-oscillator between a first state and a second state and induce aspin current in a spin channel coupled to the nano-oscillator. Themethod further includes setting, in response to the spin current, amagnetization state of a magnetoresistive device coupled to the spinchannel.

In one example, the disclosure describes a logic device including a spinchannel to transport a spin current, and a nano-oscillator having amagnetization state that, in response to an input voltage or current,oscillates between a first state and a second state and induces the spincurrent within the spin channel. The logic device also includes amagnetoresistive device that receives the spin current from thenano-oscillator, the magnetoresistive device having a magnetizationstate that is set based at least in part on the received spin current,and a controller configured to measure the resistivity of themagnetoresistive device and output a voltage or current.

In some examples, the disclosure describes a method for generating andamplifying a spin current. The method includes applying an input voltageor current to a nano-oscillator to oscillate a magnetization state ofthe nano-oscillator between a first state and a second state and inducea spin current in a spin channel coupled to the nano-oscillator,applying a gate voltage or current to the spin-channel to amplify aninput current received by the spin channel with the spin current, andoutputting the amplified current.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure.

FIG. 2 is block diagrams illustrating an example of a magnetoresistivedevice.

FIGS. 3A-3C are block diagrams illustrating an example of anano-oscillator in accordance with one or more aspects of the presentdisclosure.

FIG. 4 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure.

FIG. 5 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure.

FIG. 6 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure.

FIGS. 7A-7B are block diagrams illustrating an example of a spin logicdevice in accordance with one or more aspects of the present disclosure.

FIG. 8 is a flowchart illustrating operation of an example spin-basedlogic device in accordance with one or more aspects of the presentdisclosure.

FIG. 9 is a flowchart illustrating operation of an example spin-basedlogic device in accordance with one or more aspects of the presentdisclosure.

DETAILED DESCRIPTION

In spintronic systems, an input device sets the magnetization state ofone or more output magnetoresistive devices. In some examples, themagnetization state represents a digital bit value (e.g., a parallelstate or low resistance state represents a digital zero and ananti-parallel state of a high resistance state represents a digital one,or vice-versa). The digital value represented by the magnetization stateof the magnetoresistive devices may be considered as an output, and inthis sense, the magnetoresistive devices may be considered as outputdevices.

Spin pumping is one example way in which an input device sets themagnetization state of the one or more magnetoresistive devices. In spinpumping, the input device is coupled to a spin channel, and the one ormore magnetoresistive devices are also coupled to the spin channel. Theinput device injects (or outputs) a spin-polarized current into the spinchannel, and the one or more magnetoresistive devices receive thespin-polarized current. The spin-polarized current sets themagnetization state of the magnetoresistive devices based on the spinstate of the electrons of the spin-polarized current. For instance, ifthe spin state of the electrons is a first (e.g., up) spin state, thenthe spin-polarized current sets the magnetization state of themagnetoresistive devices to a first (e.g., up) state, and if the spinstate of the electrons is a second (e.g., down) spin state, then thespin-polarized current sets the magnetization state of themagnetoresistive devices to a second (e.g., down) state.

As described in more detail below, in the techniques described thisdisclosure, the input device that generates the spin-polarized currentmay be a type of a magnetoresistive device referred to as a SpinTransfer Torque (STT) nano-oscillator. The nano-oscillator may include asingle magnetic layer, which may include a plurality of magneticsub-layers. The nano-oscillator may include two magnetic layers thatsandwich a non-magnetic layer (e.g., an insulator layer), where themagnetic direction of one of the magnetic layers is fixed (referred toas the fixed layer), and the magnetic direction of the other magneticlayer can be set (referred to as the free layer). One of thecharacteristics of the nano-oscillator may be that, in response toapplication of a voltage or current, the magnetic direction of the freelayer oscillates permanently. The oscillation axis can be set utilizingthe magnetic anisotropy or local magnetic field. The frequency of theoscillation may be tuned based on the amplitude of the voltage orcurrent applied to the nano-oscillator.

The magnetic direction of the fixed layer of the nano-oscillator may befixed to a first (e.g., up) direction. When the direction of the freelayer of the nano-oscillator is set to the first (e.g., up) direction,the magnetization state of the nano-oscillator may be considered asbeing in a parallel state. When the direction of the free layer of thenano-oscillator is set to the second (e.g., down) direction, themagnetization state of the nano-oscillator may be considered as being inan anti-parallel state. Accordingly, in response to application of avoltage or current, the nano-oscillator may oscillate somewhere betweenthe parallel and anti-parallel states.

When oscillating, the nano-oscillator generates a spin-polarized currentin the spin channel that flows through the spin channel to one or moremagnetoresistive devices. The spin-polarized current sets themagnetization states of the one or more magnetoresistive devices, asdescribed above. Similar to the nano-oscillator, these one or moremagnetoresistive devices may include a fixed magnetic layer and a freemagnetic layer that sandwich an insulator (e.g., nonmagnetic) layer.However, the direction of the free layer of these magnetoresistivedevices may not oscillate in response to application of a voltage orcurrent.

Setting the magnetization state of one or magnetoresistive devices maybe useful for various applications. As one example, the magnetizationstates of the magnetoresistive device may indicate a digital value, andthe one or more magnetoresistive devices may be formed to function aslogical gates (e.g., NOT gates, AND gates, OR gates, etc.). For purposesof illustration, the description is described with respect to the one ormore magnetoresistive devices forming logical gates, but the spinpumping techniques utilizing a nano-oscillator, as described in thisdisclosure, are not limited to logical gates.

FIG. 1 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure. Spinlogic device 100 may include at least one input device 105, at least oneoutput magnetoresistive device 115, and spin channel 112. Input device105 may include a Spin Transfer Torque (STT) nano-oscillator 105. In thetechniques described in this disclosure, input device 105 may generate aspin current in spin channel 112 through a process known as spinpumping. In some examples, the magnetization state of outputmagnetoresistive device 115 may indicate a logical value (e.g., 0 or 1)and the magnetization state may be set based on the spin currentgenerated by nano-oscillator 105.

Nano-oscillator 105 and magnetoresistive device 115 are coupled to spinchannel 112, all of which are described in more detail below. In someexamples, the impedance, or resistivity, of input device 105 may be verydifferent than the impedance of spin channel 112. As a result, there isan impedance mismatch at the boundary between input device 105 and spinchannel 112.

In the techniques described in this disclosure, nano-oscillator 105 maybe type of a magnetoresistive device with the characteristic that themagnetization state of nano-oscillator 105 oscillates between states inresponse to a current flowing through nano-oscillator 105. Theoscillation of the magnetization state of nano-oscillator 105 induces aspin current in spin channel 112, and the spin current in spin channel112 sets a magnetization state of magnetoresistive device 115.

In the techniques described in this disclosure, when nano-oscillator 105is used to generate the spin current, the spin pumping effect induces aspin-current directly into spin channel 112. Because the spin current isinduced due to the oscillation of the magnetization state ofnano-oscillator 105, the spin current does not interact with theboundary between nano-oscillator 105 and spin channel 112. Accordingly,even if there is an impedance mismatch at the boundary, the creation ofthe spin current is not affected. Therefore, there may be relative highefficiency in the amount of spin-polarized current injected into spinchannel 112.

For instance, in other spin-based logic devices that do not usenano-oscillator 105 and instead rely on a non-oscillating input device,the impedance mismatch between the non-oscillating input device and spinchannel 112 makes it difficult to generate a sufficient amount of spincurrent in the spin channel. For instance, if a non-oscillating inputdevice is used to generate the spin-polarized current that sets themagnetization state for the one or more output magnetoresistive devices,then an impedance mismatch between such a non-oscillating input deviceand the spin channel inhibits the amount of spin-polarized current thatis injected into and that flows through the spin channel.

Furthermore, a spin-polarized current generated from a non-oscillatinginput device flows through the spin channel to the outputmagnetoresistive devices due to diffusion. However, there may not bepractical ways to control the direction in which the spin-polarizedcurrent diffuses meaning that there is a chance that an outputmagnetoresistive device does not receive the spin-polarized current.Also, the diffusion is comparatively slow, and the amount of time ittakes the spin-polarized current to diffuse to the outputmagnetoresistive device may be too long for high speed spintronicsystems.

The spin-polarized current generated by nano-oscillator 105 flows to themagnetoresistive device 115 due to both drift and diffusion forcesrather than diffusion alone. The drift force may allow thespin-polarized current to set the magnetization states of themagnetoresistive devices 115 faster than the diffusion, making thespin-polarized current generated by nano-oscillator 105 to be bettersuited for high speed spintronic systems.

In addition to minimizing the negative effects of impedance mismatch andachieving the benefits of using drift force rather than diffusion,generating the spin current using nano-oscillator 105 may also providefor scalability in generating the spin current. For instance, the sizeof the nano-oscillator 105 can be scaled for system designs allowing forrelatively small sized nano-oscillator 105 to efficiently induce spincurrent in the spin channel 112 for setting magnetization state ofoutput magnetoresistive device 115.

For example, some other spin pumping techniques use a microwave basedcoplanar waveguide to excite magnetization dynamics in amagnetoresistive device (i.e., a microwave flowing through the coplanarwaveguide induces magnetization dynamics in the magnetoresistive elementand injects a spin current in a spin channel). Microwave based coplanarwaveguide spin pumping techniques (e.g., waveguide-based spin logicdevices) may address the negative effects of impedance mismatch anddiffusion. However, microwave based coplanar waveguide devices require alarge area, and increasing the amount of spin current requiresincreasing the length of the waveguide. Thus, waveguide-based spin logicdevices require additional devices (e.g., coplanar waveguide), whichrequires significantly more total area. Waveguide-based spin logicdevices also require an external magnetic field to tune the frequency ofthe spin pumping current. Further, waveguides do not excitemagnetization dynamics efficiently (i.e., do no set magnetization statesefficiently), thus waveguide-based spin logic devices are not veryenergy efficient.

The disclosure describes a spin pumping device using nano-oscillator105, where the spin current induced in spin channel 112 is due to theoscillation of the magnetization state of nano-oscillator 105.Nano-oscillator 105 may require less power and area than waveguide basedspin pumping devices. Accordingly, the described spin pumping spin logicdevice may be more energy efficient than waveguide based devices. Thedescribed device may also occupy less chip space than waveguide basedspin logic devices, thus allowing more logic devices on the same sizedchip. Furthermore, as described above, the described device may not beimpacted by the impedance mismatch and may utilize the drift force forsetting magnetization state of output magnetoresistive device 115.

As illustrated, nano-oscillator 105 and output magnetoresistive device115 may be coupled to spin channel 112. Spin channel 112 carries a spincurrent from the at least one nano-oscillator 105 to the at least oneoutput magnetoresistive device 115. In some examples, spin channel 112may include Tantalum (Ta), Tungsten (W), or other materials with stronga spin-orbit coupling. In other examples, spin channel 112 may include atopological insulator such as Bi2Se3 or Bi2Te3.

In some examples, nano-oscillator 105 is a type of a magnetoresistivedevice. Nano-oscillator 105 may include a single magnetic layer, whichmay include a plurality of magnetic sub-layers. In some examples,nano-oscillator 105 may include a plurality of layers, including fixedmagnetic layer 106, non-magnetic layer 108, and free magnetic layer 110.Fixed layer 106 and free layer 110 may each be considered a differentside of nano-oscillator 105. Nano-oscillator 105 may include a SpinCurrent Spin Valve (SCSV). In some examples, an SCSV may includemagnetoresistive device with thinner layers than traditionalmagnetoresistive devices, as described in FIGS. 3A-3C.

Fixed layer 106 may include a ferromagnetic material (e.g., CoFeB). Asdescribed below and illustrated in FIGS. 3A-3C, in some examples, fixedlayer 106 may include a plurality of sub-layers. Free layer 110 mayinclude a ferromagnetic material (e.g., CoFeB). As described andillustrated in FIG. 3C, in some examples, free layer 110 may include aplurality of sub-layers, which may be exchange coupled.

Non-magnetic layer 108 may be sandwiched between fixed layer 106 andfree layer 110. In some examples, non-magnetic layer 108 may includeinsulating materials such as magnesium oxide (MgO). Non-magnetic layer108 may be thin enough (approximately 1.0 nanometers) that electrons maytunnel from fixed layer 106 to free layer 110, or vice versa. In someexamples, non-magnetic layer 108 may include a tunneling layer (e.g., inan MTJ). In some examples, non-magnetic layer 108 may include a spacerlayer (e.g., in a GMR).

Either side of nano-oscillator 105 may be coupled to another device orcomponent. As illustrated in FIG. 1, in some examples, a first side(e.g., fixed layer 106) may be coupled to voltage source (V_(in)) 101and a second side (e.g., free layer 110) may be coupled to spin channel112.

Fixed layer 106 and free layer 110 may include a magnetizationdirection. The magnetization direction of fixed layer 106 may be fixedso that the magnetization direction of fixed layer 106 does not change.The magnetization direction of free layer 110 may be changeable, asdescribed below.

Nano-oscillator 105 may include an operation state, such as a parallel(P) magnetization state or an anti-parallel (AP) magnetization state.The operation state of nano-oscillator 105 may depend upon themagnetization direction of fixed layer 106 and free layer 110.

The magnetization orientation of fixed layer 106 and free layer 110 maybe in-plane or perpendicular. In examples with in-plane orientation, themagnetization direction of fixed layer 106 and the magnetization of freelayer 110 are in the plane of spin channel 112. In examples ofperpendicular orientation, also known as out-of-plane, the magnetizationdirection of fixed layer 106 and the magnetization of free layer 110 arenormal to the plane of spin channel 112.

In some examples, output magnetoresistive device 115 may include aplurality of layers including fixed layer 116, non-magnetic layer 118,and free layer 120. In some examples, output magnetoresistive device 115may be similar to nano-oscillator 105. For instance, fixed layer 116corresponds to fixed layer 106, non-magnetic layer 118 corresponds tonon-magnetic layer 108, and free layer 120 corresponds to free layer110. However, the magnetization state of output magnetoresistive device115 may not oscillate in the manner that the magnetization state ofnano-oscillator 105 oscillates.

In the techniques described in this disclosure, the magnetization stateof output magnetoresistive device 115 represents a digital value (e.g.,0 or 1). For example, the impedance (also referred to as the resistance)of output magnetoresistive device 115 indicates whether the layers ofoutput magnetoresistive device 115 are aligned parallel (P) oranti-parallel (AP). In some examples, if the impedance measurementindicates high impedance, output magnetoresistive device 115 may bealigned anti-parallel, and if the impedance measurement indicates lowimpedance, output magnetoresistive device 115 may be aligned parallel.The high impedance of output magnetoresistive device 115 may correspondto a digital high, and the low impedance of output magnetoresistivedevice 115 may correspond to a digital low, or vice-versa. In otherwords, when the magnetization state of output magnetoresistive device115 is parallel (i.e., the magnetization directions of fixed layer 116and free layer 120 is the same), the impedance of outputmagnetoresistive device 115 may be low. When the magnetization state ofoutput magnetoresistive device 115 is anti-parallel (i.e., themagnetization directions of fixed layer 116 and free layer 120 areopposite), the impedance of output magnetoresistive device 115 may behigh. Low impedance of magnetoresistive device 115 may correspond to adigital low and high impedance of magnetoresistive device 115 maycorrespond to a digital high, or vice-versa.

In operation, the magnetization state of nano-oscillator 105 and thedirection of free layer 110 may be set based upon an input voltageV_(in) 101 and its corresponding current 102 (e.g., a direct (DC)current, I_(in)). The input voltage causes a current to flow intonano-oscillator 105. The current may excite magnetization dynamics innano-oscillator 105, such that the magnetization direction of free layer110 precesses (or oscillates). The oscillation of free layer 110 causesnano-oscillator 105 to oscillate. Since the resistance ofnano-oscillator 105 is a function of its magnetization state, theresistance of nano-oscillator 105 oscillates as the magnetizationdirection of free layer 106 oscillates.

In some examples, spin pumping may occur after only a few precessions ofthe magnetization dynamics. After sufficient precessions of themagnetization dynamics, spin pumping may cause a spin current to beinjected directly into spin channel 112. The Inverse Spin-Hall Effect(ISHE) may separate, based on the spin orbit, the spin up polarizedelectrons from the spin down polarized electrons, causing the spin upelectrons and spin down electrons to scatter in different directions.The drift force may then drive the spin current toward outputmagnetoresistive device 115. In some examples, the direction of the spincurrent in spin channel 112 may depend on the direction of the DCcurrent, and reversing the direction of the DC current may reverse thedirection of the spin current.

In some examples, nano-oscillator 105 includes an SCSV where free layer110 is thinner than the free layer in traditional magnetoresistiveresistive devices. As the thickness of free layer 110 decreases, themagnitude (also called the absolute value) of the output voltage atoutput magnetoresistive device 115 exhibits an asymmetric ornonreciprocal behavior for spin currents with a magnetic field havingopposite signs but identical absolute value. In other words, two spincurrents having identical frequencies but traveling in oppositedirections (i.e., traveling through oppositely polarized magneticfields, e.g., 400 Oe and −400 Oe) will produce output voltages that aredifferent in sign and magnitude. In some examples, when the spin currentfrequency is approximately 2 GHz and the spin current travels through a−400 Oe magnetic field, the output voltage may be approximately +30 μV;but, when the spin current frequency is approximately 2 GHz and the spincurrent travels through a −400 Oe magnetic field, the output voltage maybe approximately +10 μV. This asymmetric behavior increases withdecreasing film thickness.

In the illustrated example of FIG. 1, the spin current with a first spinstate (e.g., spin up) polarization flows to the right of nano-oscillator105 while the spin current with a second spin state (e.g., spin down)polarization flows to the left of nano-oscillator 105; in some examples,the spin current may flow left when polarized as spin up and flow rightwhen polarized as spin down. In the illustrated example, the verticalarrows are the same length throughout spin channel 112, illustrating thefact that the spin current does not diffuse.

As the spin current flows towards through spin channel 112 it may beabsorbed by output magnetoresistive device 115. In some examples, whenthe spin current is absorbed by output magnetoresistive device 115, themagnetization direction of free layer 120 changes. As a result, themagnetization state of output magnetoresistive device 115 may changefrom P to AP (or vice versa). In some examples, if the spin state of thespin current is a first spin state (e.g., spin down or spin up), thenthe spin-polarized current sets the magnetization state of outputmagnetoresistive device 115 to a first state (e.g., parallel oranti-parallel), and if the spin state of the electrons is a second spinstate, then the spin-polarized current sets the magnetization state ofoutput magnetoresistive device 115 to a second state.

The magnetization state of output magnetoresistive device 115 may bedetermined by reading the impedance of output magnetoresistive device115. In some examples, reading the impedance of output magnetoresistivedevice 115 may include applying a known voltage and current to outputmagnetoresistive device 115 and measuring the resistance of outputmagnetoresistive device 115. For example, if the impedance measurementindicates high impedance, output magnetoresistive device 115 may bealigned anti-parallel, and if the impedance measurement indicates lowimpedance, output magnetoresistive device 115 may be aligned parallel,or vice-versa. The high impedance of output magnetoresistive device 115may correspond to a digital high and the low impedance of outputmagnetoresistive device 115 may correspond to a digital low, orvice-versa.

In some examples, where nano-oscillator 105 includes a SCSV, the outputvoltage from output magnetoresistive device 115 may exhibit anonreciprocal behavior. In these examples, reducing the thickness offree layer 110 may allow logic device 100 to output voltages that aredifferent in direction and magnitude by maintaining the magnitude of theDC current but simply changing the direction of the DC current.

In some examples, the magnetization state of output magnetoresistivedevice 115 may be set based on voltage-controlled magnetic anisotropy(VCMA), strain induced magnetization switching, and/or exchange biasingmagnetization switching. For example, a gate voltage (and hence anelectric field) may be applied to output magnetoresistive device 115.VCMA may originate from spin-dependent screening of an electric fieldwhich leads to changes in the surface magnetization and the surfacemagnetocrystalline anisotropy. In some examples, the use of VCMA mayreduce the amount of spin current required to change the magnetizationdirection of free layer 120, thus reducing the current and voltagenecessary to cause precession in nano-oscillator 105. Reducing thevoltage and current applied to nano-oscillator 105 may improve theenergy efficiency of logic device 100. In some examples, the gatevoltage may also be utilized as a clock signal to synchronize the logiccircuit in multi-state logic circuits.

In operation, spin logic device 100 may include three phases: 1) a readphase, 2) a write phase, and 3) a standby phase. During the read phase,spin logic device 100 may determine the magnetization state of outputmagnetoresistive device 115. In some examples, determining themagnetization state of output magnet 105 may include applying a knownvoltage and current to output magnetoresistive device 115 andcalculating the resistance of the output magnetoresistive device 115.

In some examples, the write phase may include several sub-steps. First,input voltage 101 may be applied to nano-oscillator 105. The current 102(e.g., a direct (DC) current) corresponding to the input voltage 101 mayflow into fixed layer 106 of nano-oscillator 105. The current may excitemagnetization dynamics and magnetization precession in free layer 110.After sufficient precessions, spin pumping may occur such that the spinpumping may inject a spin current in spin channel 112. Then, the driftforce may drive the spin current through the spin channel 112. Outputmagnetoresistive device 115 may absorb (e.g., receive) the spin currentwhich may cause the magnetization state of output magnetoresistivedevice 115 to change. The write phase ends when input voltage 101 isremoved from nano-oscillator 105 such that the spin current can nolonger flow through the spin channel.

Spin logic device 100 resides in the standby phase when it is not in theread phase or the write phase. In the standby phase, input voltage 101is removed and free layer 110 of nano-oscillator 105 returns to itspreset magnetization direction. Spin logic device 100 then remains inthe standby phase until executing either the read phase or write phase.

As illustrated in FIG. 1 and described in more detail, spin logic device100 comprises a NOT gate. However, other examples may include differentlogical structures, such as AND, OR, NAND, NOR, etc. As illustrated bythe NOT gate in FIG. 1, when input voltage 101 is applied to thenano-oscillator (also denoted by V_(in)=1), the input voltage 101 andcorresponding input current 102 excites the magnetization dynamics innano-oscillator 105. Thus, spin pumping occurs when nano-oscillator 105starts precessing and the magnetization dynamics injects a spin currentinto spin channel 112. The spin current drifts toward the outputmagnetoresistive device 115 and output magnetoresistive device 115absorbs the spin current. As a result, the magnetization state of outputmagnetoresistive device 115 changes from anti-parallel to parallel.Thus, output magnetoresistive device 115 has a low resistance and outputvoltage 104 indicates a logical 0 (also denoted by V_(out)=0).

When input voltage 101 is removed from nano-oscillator 105 (denoted asV_(in)=0), current does not flow to nano-oscillator 105 and themagnetization dynamics in nano-oscillator 105 are not excited. Spinpumping does not occur, nano-oscillator 105 does not precess, and no thespin current is not generated. As a result, the magnetization state ofoutput magnetoresistive device 115 does not change (i.e., it remains inthe anti-parallel state). Thus, output magnetoresistive device 115 has ahigh resistance and output voltage 104 indicates a logical 1 (denoted byV_(out)=1).

The described spin pumping spin logic device may include severaladvantages over current state of the art devices. One possible advantagerelates to the size of nano-oscillator 105. Conventionalmagnetoresistive devices used in memory applications require a minimumthickness of the individual layers (typically, the minimum thickness isapproximately 10 nanometers). In contrast, in some examples, the layersof nano-oscillator 105 can be much thinner than traditionalmagnetoresistive devices because nano-oscillator 105 is not used asmemory. Spin-based logic device 100 may also occupy less area than awaveguide-based logic device. This may allow more logic devices 100 tobe placed on the same sized chip. Further, spin pumping occurs moreeasily because nano-oscillator 105 only requires a few short pulses ofcurrent to excite magnetization dynamics and cause the magnetizationdirection to oscillate. As a result, nano-oscillator 105 may requireless energy than coplanar waveguide based logic devices, such that logicdevice 100 may be more energy efficient than waveguide based devices. Inaddition, the use of spin pumping makes it so that the direction of thespin current can be controlled by directly injecting the spin currentinto spin channel 112. Thus, spin pumping spin logic device 100 mayutilize the asymmetry of the spin current spin valve (SCSV).

FIG. 2 is block diagrams illustrating an example of a magnetoresistivedevice. Magnetoresistive device 205 may include a giantmagnetoresistance (GMR) device, a magnetic tunnel junction (MTJ) device,tunneling magentoresistance (TMR) device, or the like. Magnetoresistivedevice 205 includes a plurality of layers, including fixed layer 206,non-magnetic layer 208, free layer 210, and spin channel 212, assubstantially described with reference to FIG. 1 (elements 105, 106,108, 110, and 112 respectively). Magnetoresistive device 205 includes amagnetization state that is set based on the magnetization directions offixed layer 206 and free layer 210. The magnetization state ofmagnetoresistive device 205 may be an anti-parallel configuration or aparallel configuration.

Magnetoresistive devices are often used in memory/storage devices suchas magnetoresistive random access memory (MRANI). In storage devices,fixed layer 206 and free layer 210 typically have a minimum thicknessbetween three nanometers and ten nanometers. Thinner layers may improvethe energy required to switch the magnetization direction of free layer210; however, thinner layers may be detrimental to the nonvolatilestorage capabilities of magnetoresistive device 205. Nano-oscillators105 (described above) and 305 (described below) are used for spinpumping. As a result, spin pumping nano-oscillators 105 and 305 can bemade much thinner that traditional magnetoresistive device 205. Forexample, rather than utilizing magnetoresistive device 205 forgenerating the spin current, the techniques described in this disclosureutilize spin pumping nano-oscillators that are smaller in size, andprovide better spin pumping effect as described above.

FIGS. 3A-3C are block diagrams illustrating an example of anano-oscillator in accordance with one or more aspects of the presentdisclosure. Nano-oscillator 305 may include a spin pumping effect, whichmay be used to generate (e.g., induce) a spin current in a spin channel(e.g., element 112 in FIG. 1). Nano-oscillator 305 may include aplurality of layers substantially similar to nano-oscillator 105 asdescribed in FIG. 1. For instance, nano-oscillator 305 may include afixed layer 306, non-magnetic layer 308, and free layer 310 (elements105, 106, 108, and 110 respectively). FIGS. 3A-3C illustrate electrode322 on top of fixed layer 306. In some examples, fixed layer 306 andfree layer 310 may each be considered a different side ofmagnetoresistive device 305. As such, fixed layer 306 and free layer 310may be thinner than the corresponding layers in conventionalmagnetoresistive devices. By reducing the thickness of nano-oscillator305, nano-oscillator 305 may be used for spin pumping. Spin pumpingnano-oscillator 305 may be smaller and more energy efficient than otherspin pumping methods (e.g., waveguide based devices).

Fixed layer 306 may include a ferromagnetic material (e.g., CoFeB)having a magnetization direction. As illustrated in FIGS. 3A-3C, in someexamples, fixed layer 306 may include a plurality of sub-layers. In someexamples, the sub-layers may form a Synthetic AntiferromagneticStructure (SAF).

As illustrated in FIGS. 3A-3C, fixed layer 306 may include ananti-ferromagnetic sub-layer 306A, pinning sub-layer 306B, polarizersub-layer 306C, and reference ferromagnetic sub-layer 306D. As shown inFIGS. 3A-3C, fixed layer 306 includes four sub-layers; however, fixedlayer 306 may include more or fewer sub-layers. As illustrated in FIGS.3A-3C, the approximate thickness of each layer is given in nanometers.

In some examples, anti-ferromagnetic sub-layer 306A may include anantiferromagnetic layer or synthetic antiferromagnetic material such asPlatinum Manganese (PtMn), Iridium Manganese (IrNm), or materials withsimilar properties. Anti-ferromagnetic sub-layer 306A may include athickness of approximately 10 nanometers, as illustrated in FIGS. 3A-3C.

Pinning sub-layer 306B may include a magnetic material such as IronCobalt (CoFe), Cobalt (Co), [Cobalt (Co)/Pallidium (Pd)] multilayer, ormaterials with similar properties. In some examples, as illustrated inFIG. 3A, pinning sub-layer 306B may include a thickness of approximately2.3 nanometers.

Polarizer sub-layer 306C may include Tantalum (Ta), Ruthenium (Ru), ormaterials with similar properties. As illustrated in FIGS. 3A-3C, insome examples, the thickness of electrode sub-layer 306C may include athickness of approximately 0.8 nanometers.

Reference ferromagnetic sub-layer 306D may include a ferromagneticmaterial such a Cobalt Iron Boron (CoFeB) or materials with similarproperties. As illustrated in FIGS. 3A-3C, in some examples, sub-layer306D may include a thickness of approximately 1.2 nanometers toapproximately 2.2 nanometers.

As illustrated in FIG. 3C, free layer 310 may include a plurality ofsub-layers. In some examples, the plurality of sub-layers may include aferromagnetic layer 310A and a YIG layer 310B. The plurality ofsub-layers may include HS-AOS switchable layer (e.g., switchable basedon helicity) and another magnetic layer (e.g., CoFeB, CoFe, etc.) thatdirectly contacts with non-magnetic layer 308. In some examples, thethickness of free layer 310 may be approximately 0.8 nanometers toapproximately 6.0 nanometers. In some examples, the thickness of freelayer 310 may be approximately 0.8 nanometers to approximately 3.4nanometers. Sub-layer 310A may include a thickness of approximately 0.8nanometers to approximately 1.4 nanometers, and sub-layer 310B mayinclude a thickness of approximately 2.0 nanometers. The combinedthickness of sub-layers 310A and 310B may approximately 3.4 nanometers.In some examples, the combined thickness of sub-layers 310A and 310B maybe approximately 6.0 nanometers. As illustrated in FIG. 3C, free layer310 includes two sub-layers; however, free layer 310 may includeadditional sub-layers.

Nano-oscillator 305 may include a magnetization state that is determinedby the magnetization directions of fixed layer 306 and free layer 310,as described in FIG. 1. In the techniques described in this disclosure,the magnetization state of nano-oscillator 305 changes or oscillatesbetween states in order to induce a spin current in spin channel 312.

The magnetization orientation of fixed layer 306 and free layer 310 maybe in-plane or perpendicular. As illustrated in FIG. 3A, in exampleswith in-plane orientation, the magnetization direction of fixed layer306 and the magnetization of free layer 310 are in the plane ofconductive channel 312. As illustrated in FIGS. 3B and 3C, in examplesof perpendicular orientation, also known as out-of-plane, themagnetization direction of fixed layer 306 and the magnetization of freelayer 310 are normal to the plane of conductive channel 312.

In some examples, as illustrated in FIG. 3C, fixed layer 310 may also becoupled to another electrode 324. Applying a voltage or current toelectrode 324 may assist in changing the magnetization orientation offree layer 310 from perpendicular to in-plane, which may assist inexciting magnetization dynamics in free layer 310 and generating a spincurrent in spin channel 312.

FIG. 4 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure. Insome examples, spin logic device 400 may include a plurality ofnano-oscillators 405A, 405B (collectively, “nano-oscillators 405”), spinchannel 412, and at least one output magnetoresistive device 415, asdescribed in FIG. 1 (elements 105, 112, and 115 respectively). Eachnano-oscillator 405 may include a plurality of layers and sub-layers asdescribed in FIGS. 3A-3C (e.g., fixed layer 406, tunneling layer 408,and free layer 410). Each nano-oscillator 405 may be a spin pump and mayinduce a spin current in spin channel 412. Output magnetoresistivedevice 415 may include a plurality of layers as described in FIG. 2. Inthe illustrated example of FIG. 4, spin logic device 400 includes twoinput nano-oscillators 405A and 405B (collectively, nano-oscillators405) and a single output magnetoresistive device 415, which includesfixed layer 416, tunneling layer 418, and free layer 420. In theillustrated example, a first nano-oscillator 405A may be initialized ina first magnetization state (e.g., parallel) and a secondnano-oscillator 405B may be initialized in a second magnetization state(e.g., anti-parallel). In some examples of a two input logic device,nano-oscillators 405 may have the same initial magnetization state. Insome examples, spin logic device 400 may include three or more inputnano-oscillators 405. In these examples, each nano-oscillator 405 may beinitialized to the same initial magnetization state (e.g., all areparallel or anti-parallel) or at least one nano-oscillator 405 may beinitialized to a first magnetization state while at least onenano-oscillator 405 may be initialized to a second magnetization state.

In operation, each of the at least one nano-oscillators 405 may be usedas a separate spin pump to generate a spin current as described inFIG. 1. An input voltage 401 or input current 402 may be applied to oneside of the at least one nano-oscillator 405, causing nano-oscillator405 to excite magnetization dynamics in free layer 410. When themagnetization dynamics are excited, free layer 410 oscillates betweenmagnetization states and a spin current may be generated in spin channel412. The spin current may flow through spin channel 412 and may beabsorbed (e.g., received) by output magnetoresistive device 415 asdescribed in FIG. 1. As a result, the magnetization state of outputmagnetoresistive device 415 may switch from a first magnetization stateto a second magnetization state. In the illustrated example, whether themagnetization state of output magnetoresistive device 415 changes maydepend on the operation of nano-oscillators 405A and 405B.

In some examples, spin logic device 400 may include a controller 430.Controller 430 may apply a known voltage and current to outputmagnetoresistive device 415 to determine the resistivity or impedance ofoutput magnetoresistive device 415. The resistivity of outputmagnetoresistive device 415 may correspond to a digital value. Forexample, when the magnetization state of output magnetoresistive device115 is parallel (i.e., the magnetization directions of fixed layer 116and free layer 120 is the same), the impedance of outputmagnetoresistive device 115 may be low. When the magnetization state ofoutput magnetoresistive device 115 is anti-parallel (i.e., themagnetization directions of fixed layer 116 and free layer 120 areopposite), the impedance of output magnetoresistive device 115 may behigh. In some examples, when the magnetization state is parallel theimpedance may be high and when the magnetization state is anti-parallelthe impedance may be low. Low impedance of magnetoresistive device 115may correspond to a digital low and high impedance of magnetoresistivedevice 115 may correspond to a digital high, or vice-versa. Thus,controller 430 may output an output voltage V_(out) 404 that representsa digital value based on the measured impedance of outputmagnetoresistive device 415.

As illustrated in FIG. 4, in operation, V_(out) 404 may be a function ofV_(in1) 401 and V_(in2) 401, which are given the same reference numeralto indicate that they may be similar, as well as the initialmagnetization configuration of the layers 410 and 420. As illustrated,V_(in1) and V_(in2) output respective currents I_(in1) and I_(in2) 402.Assuming that all the fixed layers (406 and 416) are toward right andfree layer 410 and 420 point toward left and right, respectively. Inthis case, magnetoresistive devices 405A and 405B are in antiparallelstate (high resistive state) and device 415 (output) is in parallelstate (low resistive state). Application of either of input voltages 401injects spin current into the channel 412 and may switchmagnetoresistive device 415 into high resistive state. The Boolean logicmay be represented by the following equation (for the configurationgiven in FIG. 4):V _(out) =V _(in1) +V _(in2)which is an OR gate.

The following table shows the relationships between V_(in1), V_(in2),and V_(out) for the example gate illustrated in FIG. 4:

V_(in1) V_(in2) V_(out) 1 1 1 1 0 1 0 1 1 0 0 0When the V_(in1) and V_(in2) are at state zero, the output voltageV_(out) is preserved at low resistive state.

In other words, when the V_(in1) is a logical high (V_(in1)=1), themagnetization dynamics in nano-oscillator 405A are excited and themagnetization state of nano-oscillator 405A begins to oscillate. Theoscillation produces a spin current in spin channel 412 that flows fromnano-oscillator 405A to output magnetoresistive device 415. Likewise, ifV_(in2) is a logical high (V_(in2)=1), the magnetization dynamics innano-oscillator 405B are excited and the magnetization state ofnano-oscillator 405B begins to oscillate. The oscillation produces aspin current in spin channel 412 that flows from nano-oscillator 405B tooutput magnetoresistive device 415. Output magnetoresistive device 415absorbs the spin current from either of nano-oscillators 405A and 405B.The current density from either of oscillator is large enough to switchthe free layer of device 415. As a result, the magnetization state ofmagnetoresistive device 415 may change such that V_(out) for spin logicdevice 400 is a logical high state (V_(out)=1).

By combining the NOT gate in FIG. 1 and the gate shown here (OR), it ispossible to implement any Boolean expression. For example, thetechniques described in this disclosure may be extendable for differenttypes of logic gates such as AND gates, NAND gates, XOR gates, etc.

One of the advantages of the magnetoresistive based logic is itsreconfigurability. The initial magnetization state of the individualfree layers 410 of devices 405A and B as well as the output free layer420 can be independently defined before logic operation. This phase isusually called as logic programing and sometimes these devices are namedas field programmable logic devices (FPLD). For example, by putting theoutput free layer 420 of the magnetoresistive device 415 intoantiparallel state similar to free layer 410 of the input devices 405Aand 405B, the output state is not affected by the inputs.

FIG. 5 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure. Insome examples, spin logic device 500 may include at least onenano-oscillator 505 and a plurality of output magnets 515.Nano-oscillator 505 and output magnetoresistive device 515 may include aplurality of layers as described in FIG. 1. In the illustrated exampleof FIG. 5, spin logic device 500 includes one nano-oscillator 505 andtwo output magnetoresistive devices 515A and 515B (collectively,magnetoresistive devices 515) that each include fixed layer 516,tunneling layer 518, and free layer 520. By applying an input voltage501 (V_(in)) or input current 502 (I_(in)) to nano-oscillator 505, whichincludes fixed layer 506, tunneling layer 508, and free layer 510, themagnetization state of nano-oscillator 505 may oscillate betweenmagnetization states (e.g., parallel and anti-parallel states). Thisoscillation of the magnetization states induces a spin current in spinchannel 512 that drifts through spin channel 512 due to the drift force,rather than traveling through spin channel 512 due to diffusion. If thespin current is polarized spin up electrons, the spin up current mayflow one direction. If the spin current is polarized with spin downelectrons, the spin down current may flow in another direction. Thus,nano-oscillator 505 may selectively change the magnetization state ofoutput magnetoresistive device 515A or 515B, depending on the directionof the spin current.

In some examples, spin logic device 500 includes at least one controller530. Controller 530 may apply a known voltage and current to each outputmagnetoresistive device 515 and determine the resistivity or impedanceof each output magnetoresistive device, as described with reference toFIG. 4 (e.g., based on the outputs V_(out1) 504 and V_(out2) 504). Basedon the measured resistivity, controller 530 may output a digital valuethat corresponds to the resistivity of magnetoresistive device 515. Theillustrated example includes separate controllers for each outputmagnetoresistive device 515; however, a single controller 530 maydetermine the resistivity two or more output magnetoresistive devices515 and output digital values that correspond to the measuredresistivity of each of the respective output magnetoresistive devices515.

FIG. 6 is a block diagram illustrating an example of a spin logic devicein accordance with one or more aspects of the present disclosure. Insome examples, spin logic device 600 may include at least onenano-oscillator 605, spin channel 612, and at least one outputmagnetoresistive device 615, as described above. FIG. 6 illustratesthree nano-oscillators 605 each including fixed layer 606, tunnelinglayer 608, and free layer 610, with electrode 603 coupled to fixed layer606. In the illustrated example of FIG. 6, spin logic device 600includes a plurality of nano-oscillators connected in series, thus spinlogic device 600 acts as a majority gate. While three nano-oscillators605 are shown in the illustrated example of FIG. 6, in general, amajority gate may include any number of nano-oscillators 605 so long asthere are at least two nano-oscillators 605. In a majority gate, theoutput value returns a true if and only if more than 50% of the inputsare true. In the illustrated example, spin current in spin channel 612may cause the magnetization state of output magnetoresistive device 615to change based on the magnetization states of the nano-oscillators 605.In some examples, when the input voltage 601 (V_(in)) and correspondingcurrent 602 (I_(in)) excites magnetization dynamics in a majority of theplurality of nano-oscillators, the excited nano-oscillators may generatesufficient spin current in spin channel 612 to cause outputmagnetoresistive device 615 to change magnetization states (e.g., fromAP to P or vice versa). As illustrated, magnetoresistive device 615includes fixed layer 616, tunneling layer 618, and free layer 620.Electrode 622 is coupled to fixed layer 616.

FIGS. 7A and 7B are block diagrams illustrating an example of anano-oscillator in accordance with one or more aspects of the presentdisclosure. In some examples, nano-oscillator 705 includes a SpinCurrent Spin Valve (SCSV). SCSV 700 may include a plurality of layerssubstantially as described in FIG. 3C. For instance, fixed layer 706(M_(P)) corresponds with fixed layer 306, non-magnetic layer 708corresponds with non-magnetic layer 308, and free layers 710A and 710B(MF₁, MF₂, respectively) together correspond with free layer 310. Fixedlayer 706 and free layer 710 may include a plurality of sub-layers, asdescribed in FIG. 3C. In the illustrated example, the magnetizationorientation of fixed layer 706 and free layer 710 is shown in theperpendicular orientation. As also illustrated, voltage source 701(V_(c1)) outputs current 702 (I_(in)).

In operation, nano-oscillator 705 may operate in a similar as describedin FIG. 1. In some examples, SCSV 700 may include a voltage or exchangebias controlled gate between nano-oscillator 705 and an outputmagnetoresistive device. A gate voltage V_(g1) 704 may be applied to thespin channel 712, causing free layer 710 to transition fromperpendicular orientation to in-plane orientation. Input current I₁ maybe applied to fixed layer 706 causing precession of the magnetizationdirection of free layer 710. As free layer 710 precesses, spin currentmay be injected directly into spin channel 712. The drift and diffusionforces may cause the spin current to flow through spin channel 712,which may change the magnetization state of an output magnetoresistivedevice (not shown).

In some examples, SCSV 700 may act as a NOT or PASS gate with a gatecontrol and device configuration is in such a way that may be easilyused in cascaded devices such as a ring oscillator. For example, asgiven in FIG. 7A, magnetoresistive device 705 may perform oscillationsonly when V_(c1) is present. If V_(c1)=0, the input current I₁ in spinchannel 712 may be absorbed by free layer 710B such that I_(out)=0. WhenV_(c1)=1, free layer 710B may oscillate such that I_(out)=I₁. In someexamples, a gate voltage V_(g1) may be applied to magnetoresistivedevice 705, which may bring the magnetization MF₂ from out-of-plane intothe plane direction. Thus, free layer 710B may begin spin pumping andmay inject a spin current into the channel 712 such that I_(out) may begreater than I₁. In this example configuration, SCSV device 700 mayprovide gain on the input current (I₁), where a voltage V_(g1) isapplied to spin channel 712, as illustrated.

In some examples, an SCSV device 700 may be used as a ring oscillator.One condition for a ring oscillator is having a gate with a gain aboveone. By applying a gate voltage V_(g1) magnetoresistive device 705, SCSV700 may amplify I₁ such that I_(out) is greater than I₁. In someexamples, if V_(g1) is not present, SCSV 700 does not amplify thesignal. Instead, SCSV 700 acts as a nano-oscillator of the aboveexamples and I_(out)=I₁.

FIG. 8 is a flowchart illustrating operation 800 of an examplespin-based logic device in accordance with one or more aspects of thepresent disclosure. For purposes of illustration only, the method ofFIG. 8 will be explained with reference to the example spin logic devicedescribed in FIG. 1; however, the method may apply to other examples.

In some examples, spin logic device 100 may include nano-oscillator 105,spin channel 112, and output magnetoresistive device 115.Nano-oscillator 105 may receive an input voltage or current (802). Forexample, an external source may apply an input voltage or current tonano-oscillator 105. The input voltage or current may excitemagnetization dynamics in nano-oscillator 105 causing the magnetizationstate of nano-oscillator 105 to oscillate (e.g., AP to P, or P to AP).

After sufficient oscillations, nano-oscillator 105 may begin spinpumping (804). Spin pumping induces a spin current in spin channel 112.In other words, a spin-current is induced by nano-oscillator 105. Insome examples, the voltage or current applied to nano-oscillator 105 maybe removed once the spin current is induced in spin channel 112;however, the techniques described in this disclosure are not so limited.The spin current may flow through spin channel 112 due to diffusion.

Output magnetoresistive device 115 may absorb or receive the spincurrent from spin channel 112 (806). As a result, the magnetizationstate of output magnetoresistive device 115 may change from AP to P, orvice versa (808).

The magnetization state of output magnetoresistive device 115 may bedetermined (810). The magnetization state may be determined by applyinga known voltage and current to output magnetoresistive device 115 andmeasuring the resistance of output magnetoresistive device 115.

FIG. 9 is a flowchart illustrating operation 900 of an examplespin-based logic device in accordance with one or more aspects of thepresent disclosure. For purposes of illustration only, the method ofFIG. 9 will be explained with reference to the example spin logic devicedescribed in FIGS. 7A and 7B; however, the method may apply to otherexamples.

As described above with reference to FIG. 7A and 7B, nano-oscillator 705may receive an input voltage or current (902). The input voltage orcurrent may excite magnetization dynamics in nano-oscillator 705 causingthe magnetization state of nano-oscillator 705 to oscillate (e.g., AP toP, or P to AP). After sufficient oscillations, nano-oscillator 705 maybegin spin pumping (904).

A gate voltage (V_(g1)) may be applied to spin channel 712 causing freelayer 710 to transition from a perpendicular orientation to an in-planeorientation. As described above in FIGS. 7A and 7B, when the gatevoltage is applied, the current through the spin channel is amplifiedsuch that I_(out) is greater than I₁ (906). In some examples, theI_(out) current may be an input into a stage of a ring oscillator.

An output magnetoresistive device may absorb or receive the amplifiedspin current from spin channel 712 (908). For example, the outputmagnetoresistive device may be part of a ring oscillator. As a result,the magnetization state of the output magnetoresistive device may changefrom AP to P, or vice versa (910). The magnetization state of the outputmagnetoresistive device may be determined (912). The magnetization statemay be determined by applying a known voltage and current to the outputmagnetoresistive device and measuring the resistance of the outputmagnetoresistive device.

In some examples, such as those described with respect to FIGS. 7A, 7B,and 9, an output magnetoresistive device may not be necessary in everyexample. For instance, the I_(out) current, which is generated from theI₁ current and the induced spin current (which causes I_(out) to begreater than I₁), may be an input current into additional circuitry andis not necessarily limited to being absorbed by an outputmagnetoresistive device. However, in some examples, the I_(out) currentmay be absorbed by an output magnetoresistive device, and because theI_(out) current is greater than the I₁ current, the magnetization stateof the output magnetoresistive device may be set faster.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. A method comprising: applying DC input voltage or current to a nano-oscillator to oscillate a magnetization state of the nano-oscillator between a first state and a second state and induce a spin current in a spin channel coupled to the nano-oscillator; applying a gate voltage or current to the spin-channel to amplify an input current received by the spin channel with the spin current; and outputting the amplified current.
 2. The method of claim 1, wherein applying the DC input voltage or current further comprises exciting magnetization dynamics in the nano-oscillator, wherein the oscillation of the nano-oscillator between the first state and the second state induces the spin current, and wherein the spin current drifts through the spin channel.
 3. The method of claim 2, wherein the exciting magnetization dynamics is further based on one or more of voltage-controlled magnetic anisotropy (VCMA), strain induced magnetization switching, or exchange biasing magnetization switching.
 4. The method of claim 1, wherein the nano-oscillator comprises a magnetoresistive device, the magnetoresistive device comprising one of: a single magnetic layer; or multiple layers including a fixed magnetic layer, a free magnetic layer, and a non-magnetic layer.
 5. The method of claim 4, wherein the thickness of the single magnetic layer or the free magnetic layer is between approximately 0.8 nanometers and approximately 6.0 nanometers.
 6. A device comprising: a nano-oscillator; a spin channel coupled to the nano-oscillator, the spin channel configured to receive an input current and output amplified current; a first source configured to apply DC input voltage or current to the nano-oscillator to oscillate a magnetization state of the nano-oscillator between a first state and a second state and induce a spin current in the spin channel; and a second source configured to apply a gate voltage or current to the spin-channel to amplify the input current received by the spin channel with the spin current to generate the amplified current.
 7. The device of claim 6, wherein the nano-oscillator comprises a magnetoresistive device, the magnetoresistive device comprising one of: a single magnetic layer; or multiple layers including a fixed magnetic layer, a free magnetic layer, and a non-magnetic layer.
 8. The device of claim 7, wherein the thickness of the single magnetic layer or the free magnetic layer is between approximately 0.8 nanometers and approximately 6.0 nanometers.
 9. The device of claim 6, wherein the oscillation of the nano-oscillator between the first state and the second state is further based on one or more of voltage-controlled magnetic anisotropy (VCMA), strain induced magnetization switching, or exchange biasing magnetization switching.
 10. The device of claim 6, wherein the oscillation of the nano-oscillator between the first state and the second state induces the spin current, wherein the spin current drifts through the spin channel from the nano-oscillator. 